The Impact of Endometrial Thickness on the Day of Human Chorionic Gonadotrophin (hCG) Administration on Ongoing Pregnancy Rate in Patients with Different Ovarian Response

In order to explore the impact of endometrial thickness on hCG administration day on ongoing pregnancy rate (OPR) in IVF-ET cycles, we retrospectively analyzed data from 10,406 patients undergoing their first IVF cycles with standard gonadotropin releasing hormone analogue (GnRH-a) long protocol. Firstly, patients were divided into poor (≤ 5 oocytes), medium (6–14 oocytes), and high (≥ 15 oocytes) ovarian responders based on the number of oocytes retrieved. In each group, patients were sub-divided into three groups according to the endometrial thickness on the day of hCG administration: Group A, thin endometrial thickness (≤ 7 mm); Group B, medium endometrial thickness (8–13 mm); Group C, thick endometrial thickness (≥ 14 mm). (1) For poor responders, OPRs were significantly different in the three endometrial thickness groups (28.57%, 44.25%, and 51.34%; P = 0.008). The association between thin endometrial thickness and OPR was significant after controlling for age, number of embryos transferred by multivariate logistic regression analysis (adjusted OR: 0.408; 95% CI: 0.186–0.898; P = 0.026. Reference = thick endometrial thickness). (2) For medium responders, OPRs were 31.58%, 55.56%, and 63.01% (P = 0.000) in the three groups. Adjusted OR for thin endometrial thickness was 0.284 (95% CI: 0.182–0.444; P = 0.000). (3) For high responders, OPRs were also significantly different in the three groups (28.13%, 52.63%, and 63.18; P = 0.000). Adjusted OR for thin endometrial thickness was 0.233 (95% CI: 0.105–0.514; P = 0.000). For patients undergoing IVF with different ovarian response, a thin endometrium on the day of hCG administration adversely affects ongoing pregnancy rate.